1. Field of the Invention
The present invention is directed to an electromechanical motor, a method for the operation thereof.
2. Description of the Prior Art
Piezo motors are known primarily in the form of a traveling wave motors and tappet-driven piezo motors. Whereas the former must always be operated in a resonant mode, the tappet-driven piezo motor can be operated resonantly as well as non-resonantly. As advantages, a piezo motor
has a high torque because it rotates slowly, so that a translation gearing (transmission) can be eliminated;
a short acceleration and stopping time in the millisecond range;
self-inhibition, i.e. that a position of a drive shaft is preserved after turn-off, even given the influence of external forces;
a low mass, which enables a lightweight structure in, for example, a motor vehicle;
a small structural volume as a result of the unneeded translation gearing;
emission of substantially no electromagnetic stray fields;
a high efficiency; and
a possibility of load monitoring with the piezo actuator/sensor.
The disadvantages of a piezoelectric traveling wave motor are high wear due to frictional drive, high manufacturing costs due to the required mechanical precision, which must be durably implemented, a lack of scability due to the traveling wave principle thereby limiting it to a comparatively small structural size.
The disadvantages of a tappet-driven piezo motor are high wear due to frictional drive, high noise production due to the impact of a drive tappet on a shaft, high manufacturing costs caused by a high mechanical precision, and slippage, i.e. if external forces act on the shaft, the shaft is moved somewhat back in the phase wherein there is no frictional lock with the drive tappet. In order to avoid slippage, a number of piezoelectrical drive tappets can be provided, so that there is always a frictional lock between at least one of the tappets and the drive shaft. This, however, causes extremely high costs due to the required number of piezo actuators together with appertaining drive electronics.
An object of the present invention is to provide a wear-resistant, quiet, largely slippage-free and simplified motor.
This object is inventively achieved in an electromechanical motor having at least two electromechanical drive elements, a drive ring on which the drive elements act, and a driveable shaft. The drive ring is caused to perform a circulatory displacement motion as a result of a combination of linear displacements of the respective electromechanical drive elements, i.e. by controlling the linear displacement amplitudes of the individual drive elements and the relative timing of these amplitudes. A circulatory displacement motion of the drive ring means that this element is displaced along a curved path, but does not rotate or rotates only insignificantly. The curved path can, for example, be circular or elliptical but is not limited to these path shapes. The drive ring need not continuously traverse the curved path, but can be arbitrarily stopped and reversed in terms of its motion sense.
The shaft can be placed in the drive ring, or vice versa, so that the displacement motion of the drive ring can be transmitted onto the shaft due to the contact between the shaft and the drive ring. Since the drive ring proceeds on a curved path, the shaftxe2x80x94when the drive ring movesxe2x80x94is entrained in rotary fashion by frictional contact. In addition to being dependent on the rate of motion of the drive ring, the rotational speed of the shaft is also dependent on the shape of the shaft and of the drive ring, among other things.
The electromechanical drive elements can be in the form of actuators, with a displacement being produced by applying an electromagnetic signal, for example a piezoelectrically, magnetostrictively, electrostrictively or electrodynamically driven actuator.